Composite signaling system



arch 10, 1936. M, Q GODDARD 2,033,282

COMPOS ITE S IGNALING SYSTEM Filed July 14, 1933 2 Sheets-Sheet l March 10, 1936. M. c. GODDARD COMPOSITE SIGNALING SYSTEM Filed July 14, 1933 2 Sheets-Sheet 2 ATTOWV Patented Mar. 10, 1936 UNETED STATES PATENT OFFICE to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application July 14, 1933, Serial No. 680,422

1 Claim.

This invention relates to signaling systems and more particularly to systems for transmitting signals over long lines.

In systems heretofore used, particularly composite signaling circuits employing electromagnetic relays, either of the neutral or polar type, for receiving the signal impulses, a certain definite current strength is required to operate. the relay and the movement of the armature lags behind the signal impulse due to the mechanical inertia of the armature and the line constants such as inductance and capacity. This time lag increases in general as these constants increase in value. This situation is accentuated, and distortion in the received signals frequently occurs, when intermediate repeaters are inserted in the signal line.

To overcome these diificulties and secure more satisfactory operation especially under these extreme conditions, it is proposed to substitute for the electromagnetic receiving relay an arrangement comprising a pair of gas-filled discharge tubes coupled to the line by means of a transformer whereby a change in potential in one direction in the line will start a space discharge in one of the tubes which will persist until a potential change in the line occurs in the opposite direction which will start a discharge in the other tube which will stop the discharge in the first tube. By inserting a conventional relay in the plate circuit of the first tube any desired signal device can be controlled.

An object of the invention therefore is to improve the signal receiving means in systems of the character described.

Another object is to reduce distortion in the received signals.

Still another object is to permit satisfactory signal reception over longer lines than has been possible heretofore.

A further object is to reduce the current necessary for the operation of systems of the character described.

A still further object is to eliminate interference with the signals by steady state earth potential at either the transmitting or receiving station.

A feature of the invention whereby the foregoing objects are attained resides in substituting, for the electromagnetic relays heretofore used in systems of the character described, a pair of gas-filled discharge tubes and a transformer having an extra winding in addition to the windings employed in connection with the electromagnetic relays. To the midpoint of the extra transformer winding a source of negative grid potential is connected and the two winding terminals are connected to the respective grid electrodes of the pair of discharge tubes. In the plate circuit of the first tube is connected a conventional type neutral relay and the two anodes of the tubes are connected together by a circuit including a condenser. By means of this arrangement a change in the line current potential in a certain direction and flowing in a winding of the transformer causes a mo mentary current impulse to flow in the extra winding of the transformer which causes the normally negative condition of the grid of one tube to be changed to positive long enough to start a discharge between its space electrodes thereby causing the operation of the plate circuit relay in series therewith. Due to the characteristics of this tube the discharge continues until the plate current is interrupted.

The grid polarity of the second tube is not changed by this first line potential change.

During the period the first tube is discharging each plate of the condenser is positively charged to the polarity of its associated tube anode. When the potential of the line again changes, in a reverse direction, a momentary current impulse in an opposite direction to the first impulse is induced in the extra winding of the transformer thereby changing the grid potential of the second tube from negative to positive whereupon a discharge starts therein. This discharge causes the condenser plate connected to the anode of the second tube to change its potential sufiiciently to cause the opposite plate of the condenser to change from positive to negative thereby stopping the discharge of the first tube and releasing the relay.

A complete understanding of the operation of the system contemplated by the invention as well as an appreciation of its various features may be gained from a consideration of the following detailed description and the annexed drawings.

Referring now to the drawings, there is shown a two-way composite phantom trunk system providing simultaneous telephone and telegraph transmission. Y

Fig. 1 shows the equipment located in ofiice A while Fig. 2 shows the equipment of a distant office B.

Two physical telephone circuits are provided by lines L1 and L2 terminating respectively in jacks l and 2 at ofiice A and jacks 3 and 4 at ofiice B While a third telephone circuit is provided by phanto-ming, this circuit terminating at office A in jack 5 and at ofiice B in jack 6.

peating coil 34.

resistances 36 and 31 and condenser 38 is, associated with thesecond winding of repeatingcoil Condensers I, 8, 9 and III at oifice A and II, I2, I3 and I4 at ofiice B are connected in series with the lines and furnish a low impedance path to the telephone currents at the same time preventing the passage of the direct current telegraph signals. Repeating coils I5 and I6 are connected across line L1, I1 and I8 are connected across line L2 while I9 and 2|l are associated with the phantom circuit.

For initiation of the telegraph or other signals, three telegraph sending sets are shown at each station, the sets at station A including keys 2|, 22 and 23 which control respectively the operation of relays 24, 25 and 26. Associated with the armature circuits of these relays are sources of positive potential 21, 28 and 29 andsources of negative potential 30, 3| and 32. The armatures of relays 25 and 26 are associated withtherrespective windings of repeating coil 33 and with two windings of repeating coil 34 while the armature of relay 24. is associated with one winding of repeating coil-35 anda third winding ofre- A path to. ground including 35 and the fourth winding of repeating coil 34 for purposes of line balance.

The telegraph sending sets associated with station B are'similar to those of station -A, including keys 39, 40 and 4|, relays 42, 43 and '44, sources of positive potential 45,46 and and sourcesof negative potential 48,49 and 50.

Associated with station A are three telegraph receiving sets including sounders 51,-58 and'59 controlled respectively by relays 60,-6I and 62. These relays are in turn each associated with theplate circuits of a pair of gas-filled vacuum tubes. These-vacuum tubes 63, 64,35,65, 61 and 6B are of the type frequently referred to as trigger tubes and-may, for example, be constructed as described inthe copending application of A. L. Samuel filed July 1, 1930,5erial- No. 465,083. Each tube is provided with a filament heating battery 69, 19 and 'Il-swhile the -plates of each pair of tubes are connected through-a path including respectively condensers I2, 13'and 'I4. A four winding transformer 15, 16 and 1-1 is associated with each receiving set, the fourth winding of each transformer (in describingthese transformers as well as the similar transformers associated with station B, the windings will be termed, first, second, -third and fourth, starting in each instance with the winding most remote from the associated. pair of tubes) being connectedto the grids of the associated'tubes. By virtue of a source of negative potential 1 8, 79 and 80, associated with the fourth winding of each transformer, the grids of the tubes normally are negatively biased.

The telegraph receiving sets'located at station B are similar to those at station A and include 1 sounders -85, 86 and 81 controlled, respectively,

by relays '88, 89 and 90, trigger tubes 9|, 92, 93, 94, 95 and 96 and transformers I04, I05 and For purposes of line balance networks 8| and 33 are associated with line'L1 and networks 82 and 84 are associated with line L2.

Impedance coil I29 isbridged across'line L1 at station A and serves as a means'forpreventing the. flowv of alternating current telephone signals in the telegraph receiving circuit of station .A and yetpresents a low impedance path to the direct current telegraph signals. For the slight alternating current that may possibly traverse opposite.

condensers I30 and I3I are bridged across line. L2 at stations A and B respectively.

Let it now be assumed for purposes of illustration that one of the telegraph keys, say 2 I, at station A is operated in order that a signal may be producedon the associated sounder 85 at station 13. Normally, i. e., when key 2| is in unoperated position a negative potential is applied to line conductor III! from battery 30. As key 2| is operated, however, relay 24 operates and substitutes batteryd'l for battery 30 thus applying a positive potential on the line and causing a re-- versal of the line current.

state current results from the charging of condenser I32. through-repeating coils '35 and 34 .to the mid- ..point of the firstwinding of transformer 15 where the current divides, ,a part passing through the lowerhalf of the winding, through impedance: I34 and resistances|35 and I36 of the balancing;

networkto groundand the remainder passing through the .upper half. of the winding, through the upper-winding of impedance I20, line conductor Imandupper winding of impedance I23, upper half of first or rig-ht hand winding .of trans-- As battery 21 is con- -nected. to the line, amomentary positive pulse of ,currentof greater magnitude than the steady This positive .pulse of current passesv former I04 where .it divides, a part passing through repeating coils..52 and .53, armature of relay 42, negative battery 48 toground and the .remainder. passingrthrough the lower. half of the first winding of transformerIM, throughim pedance; I39 and resistances I49 and .I4l of balancingnetwork-83. to. ground. Condenser II prevents this. pulse of direct current from passing into thetelephone repeating coil-I6. Now'this mo- -mentary positive pulse of current flowing through the first windingof transformer 15 has no. inductive veifect. on. the. other windings thereof inview ofthe fact. that an equal amount of the current passes through each half of the winding, the direction of current flow through each half being about the second half. The current, however,

passes .through each half ofthe first or 1 right hand,;w inding. of transformer I94 in the same y direction thus inducing a momentary voltage in the-fourth or-left handwinding of thetransformer. This induced voltage momentarily reducesthe normal negative grid bias of tube 9| changed. in a positive direction at this time, how-y ever, in-view of the direction of flow of the inducedcur-rent.

The completion of the space current path in tube -.9I now completesa path for the operation of-relay,88:bybattery-I44. The operation of relay .188, in. turn completes the energizing path for sounder 85, from battery I46 through the winding of the.sounder\85, armature and make contact of relay: 88. to-g round I41;

The operation ofkey 2l at station A has there- 1 The fluxset upabout one half of the winding is therefore cancelled by that set up fore, in the manner described above, resulted in a corresponding operation of associated sounder 85 at station B. It is also desirable of course that the return of key 2| to normal position will at the same time result in sounder 85 restoring to normal. Such action is brought about in the following manner:

Assuming that key 2| be restored to normal, the energizing circuit of relay 24 is interrupted and the relay therefore restores to normal which in turn removes the positive source of potential 2! from the line and replaces the negative source 30. Now when battery 3|] is reconnected to the line, condenser I56 again charges and a momentary pulse of current of greater magnitude than the steady state current value is impressed on the line. This action is similar to that resulting when relay 24 was operated through the operation of key 2|, the pulse of current in this instance however being in the opposite direction. In the manner previously described in tracing the action of the positive pulse, the negative pulse of current passes through the first winding of transformer 15, having no inductive effect on the other windings, but, in passing through the first winding of transformer I94, induces a momentary potential in the fourth or grid winding of the transformer. Now due to the opposite direction of the pulse, the induced current is, in this instance, of a direction to reduce the normal negative grid bias of tube 92 towards a positive bias. As the characteristics of tube 92 are similar to those of tube 9| previously referred to, a discharge is now set up between the space electrodes of tube 92.

During the discharge of tube 9|, each plate of condenser was positively charged to the polarity of its associated tube anode. As tube 92 starts to discharge the associated plate of condenser ||l| changes its potential sufficiently to cause the opposite plate to change from positive potential to a negative potential. Due to the characteristics of tube 9|, its discharge is stopped as the positive potential of its anode is interrupted.

The interruption of the space current path in tube 9| removes the energizing circuit of relay88 which therefore restores to normal. As the energizing circuit for sounder 85 is now interrupted, the sounder also drops back to normal.

In the manner described therefore, restoring key 2| to normal has resulted in the corresponding sounder 85 also restoring to normal. From the previous description of the result of operating key 2| and the description just given of the result of restoring the key to normal, it will be apparent that the sounder is operated in step with the key. As the operation of the other sending sets and associated receiving sets is similar to that described above they will not be described in detail.

When a signal impulse passes over a conductor to the distant station, there is a momentary current flow of smaller magnitude in the other conductors of the quad due to capacity between the conductors. This current flows in the same direction as the signal at the receiving end and in the opposite direction at the sending end and, if uncorrected, gives rise to cross-fire, i. e., the fault of one telegraph sounder responding when a signal is being received by another.

In order to remedy this objectionable feature at the receiving end, the current pulses are led through a winding of either transformer 35 or 33 and a winding of transformer 34 at the sending end thereby inducing an opposing and neutralizing current flow in the other conductors of the quad at the receiving end. The line capacity currents received at the sending end over the other conductors of the quad pass through the upper half of the first windings and through the third windings of the transformers but their effect is neutralized by current flowing through the lower half of the first windings and through the second windings of the transformers due to the discharge of condensers I60, NH, 62 and I63 associated with the balancing networks.

In view of the fact that the only telegraph signals effective are those received through inductive transformer action it will be apparent that steady state earth potentials can cause no interfering signals in the receiving circuits. Earth potential surges or alternating earth potentials cause currents of equal magnitude in the upper halves of the first windings of the transformers and in the third windings which currents neutralize one another and thus cause no inductive effect in the grid windings.

No detailed description of the method of tele phone signal transmission has been given, as the transmission of such signals over phantomed circuits is well understood.

While a phantom telephone system composited for telegraph transmission has been selected for detailed description the invention is not limited in its application to such a system. For example, circuit controlling members other than telegraph keys such as means for transmitting supervisory signals or the like may be utilized at the sending end while the responsive devices at the receivin end may be other than telegraph sounders. The invention is, as a matter of fact, intended to be limited only as indicated by the attached claim.

What is claimed is:

In a composite signaling system, in combination, a pair of line circuits arranged in phantom relation, a plurality of signaling stations at each end of said lines, direct current signal transmitting means at each station including a source of positive and a source of negative potential, composite circuit means connecting each transmitting means to a different conductor of said lines, switching means for controlling the connection of either the positive or negative source to the composite circuit, receiving means at each station connected to the same composite circuit as the transmitting means, said receiving means including a pair of gas-filled discharge devices and a relay, one device being responsive to a signal impulse of one polarity transmitted from the distant station over the respective conductor to operate the relay and the other device being responsive to a; pulse of the opposite polarity to restore the relay to normal, a transformer at each station having a portion of one winding in series between the respective composite circuit and the transmitting means and another portion connected between the transmitting means and a balancing network to ground, a second winding connected to the control electrodes of the associated discharge devices and means including a third winding of all said transformers in series for preventing currents induced in the other conductors of the lines due to impulses transmitted by one station from affecting the receiving means of the other stations at the transmitting end.

MYRON C. GODDARD. 

